Analyzing the ‘aquifer’ rainfall, the precipitation which falls between mid October and mid March that percolates down into the sub strata, it has been the fifth wettest period since 1984 with 16% (63mm) above the long-term average. My new equipment enables me to see when evaporation exceeds the moisture that soaks down through the earth and I find that in March, almost 60% of the total rainfall evaporated. There has been an increasing trend in the total aquifer precipitation over the last 27 years in Marlborough, from approximately 375mm in the 1980’s to almost 440mm in the 2000’s.
Category: Commentary
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First and last frosts
In my report for May 2009 I included data on air frost and how the occurrence of below zero temperatures had changed over the years since my records began in 1984. I have now analysed the pattern for the first frost at this time of year. To see the trend more clearly I have analyzed the data over five-year periods and the average for each period is in the table below, both for Spring and Autumn. Although the warming in Spring is evident from 1985, this trend for Autumn didn’t start until the late 1990’s. For both periods there is now a shift of around one month, for these average figures.
1985 – 89
1990 – 94
1995 – 99
2000 – 04
2005 – 09
Last Frost of Spring 14th May
11th May
5th May
26 April
22nd April
First Frost of Autumn 29th Sept.
22nd Sept.
9th Oct.
18th Oct.
26th Oct.
The trend in the total degrees of air frost for each month since 1984, November & December 2009 excluded, also produces interesting data, as in the table below. November and particularly December during this period, show an increasing severity of air frost in contrast to the less severe monthly frost totals at the beginning of the year.
January
February
March
October
November
December
-8°
-10°
-3°
-1°
+3°
+20°